Sonotube Concrete Calculator
Diameter in inches, height in feet, straight to bags per tube.
Also known as tube concrete · cardboard form concrete · pier concrete
With the default inputs: Tube diameter 12 in · Pour height 4 ft · Number of tubes 4 pcs etc.Total concrete 0.51 yd³
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Result
| Tube cross-section | 0.79ft² |
| Volume per tube | 3.14ft³ |
| Bags per tube | 6bags |
| Total with waste | 13.8ft³ |
| Total cubic yards | 0.51yd³ |
| 80 lb bags | 24bags |
| Total weight | 2004lb |
How this is worked out
Tube volume is pi x (diameter/24)² x height, where diameter in inches divided by 24 gives the radius in feet directly. Pour height should be measured to the top of the tube, but in practice you stop 2-3 in short and top up after the post is set - allow for that top-up in the order. Dry tube walls and pervious subgrade drink extra mix, so start at 10% waste and go to 15% on gravel or in dry conditions.
Next up: Concrete Volume Calculator · Concrete Mix Design Calculator
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Formula
| Area = π × (D/24)² | D in inches, D/24 is the radius in feet |
| Volume per tube = area × pour height | height in feet |
| Total = per tube × count × (1 + waste) | |
| Cubic yards = ft³ ÷ 27 |
How to work it out
- Divide tube diameter in inches by 24 to get the radius in feet - diameter over 2 for radius, over 12 for feet, which combines into 24.
- Area = π × radius², so a 12 in tube is 0.785 ft² and an 8 in tube is 0.349 ft².
- Volume per tube = area × pour height in feet.
- Multiply by the number of tubes, then add 10% for dry tubes drinking mix and pervious subgrade.
- Divide by 27 for cubic yards and by bag yield for bags; round up bags per tube, not just the total.
Where it goes wrong
- Using diameter as radius - a 12 in tube calculated that way is 4x over, and the surplus is wasted.
- Measuring pour height above grade only - the buried depth has to be poured too, and in frost areas that is often half the total.
- Forgetting the 2-3 in left short and topped up after the post is set - grouting later leaves a weak bond plane.
- Rounding up the grand total instead of per tube - every tube then comes up fractionally short.
Material and cost
Fibre tubes are sold by diameter and length: an 8 in x 4 ft runs about USD 8-12 each and a 12 in x 4 ft about USD 14-20, rising steeply with diameter. Concrete inside is priced by volume, but small quantities usually mean bagged mix at USD 5-8 per 80 lb bag, so a 12 in x 4 ft tube is roughly 6 bags and USD 40-50. A complete footing - hole, tube, concrete and anchor - commonly lands at USD 80-150 with labour on top.
On site
- Ask the local building department for frost depth, not a neighbour - requirements can differ street by street.
- Put 2-3 in of gravel in the hole before setting the tube so water drains below rather than the concrete sitting in mud.
- Cover the tube top with plastic after pouring; direct sun on a fresh surface dries it out and cracks it.
Basis
- ACI 332 Residential Code Requirements for Structural Concrete (isolated footings and frost depth)
- IRC International Residential Code, Chapter R403 (footing depth and minimum size)
- ASTM C94 Standard Specification for Ready-Mixed Concrete
FAQ
How much more concrete does a 12 in tube take than an 8 in?
How deep and how long should the tube be?
Do I leave the Sonotube in the ground?
Cite this page
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Building Calculator. Sonotube Concrete Calculator. 2026-10-25. https://jianzhujisuan.com/en/sonotube-concrete